Uptake of DNA by mammalian cell will be investigated, using SV40 DNA as a prototype. Approaches to maximize specific infectivity will include use of DNA-protein complexes, liposomes, and direct infection of viable cell nuclei. The possibility of developing a practical, preparative method for separating the strands of SV40 DNA will be investigated. Restriction endonucleases and DNA-binding drugs will be employed. Experiments designed to map the initiation sites for transcription of SV40 DNA will be continued.